The present invention relates to a platinum catalyst composition which may be used as a catalyst, inter alia, of the hydrosilylation reaction, to a method for its preparation, and to a curable organopolysiloxane composition which contains said platinum catalyst composition.
A large number of platinum compounds are known as hydrosilylation reaction catalysts. Among these, the platinum/alkenylsiloxane complex catalyst compositions as disclosed in Japanese Patent Publication Number 42-22924 (22,921/67) and Japanese Patent Publication Number 46-28795 (28,795/71) have a high catalytic activity and are useful as hydrosilylation reaction catalysts. These are prepared by a reaction, for example, between alkenyl group-containing siloxane and chloroplatinic acid.
However, this type of platinum catalyst composition generally suffers from a poor storage stability, and, unless careful attention is paid to its method of storage, it readily deteriorates into platinum black with a concomitant substantial loss in catalytic activity. For example, the catalyst suffers from a loss in activity within a few hours merely upon an increase in storage temperature. Moreover, its storage stability is also sharply reduced by other substances which may be compounded into the reaction system.
A large number of methods have been introduced in order to solve these problems For example. Japanese Patent Publication Number 47-23679 (23,679/72) proposes that the storage stability be increased by removing the halide in the prepared platinum/alkenylsiloxane complex catalyst composition. In this method, the platinum/alkenylsiloxane complex catalyst composition is stored as such or in a neutral medium such as polysiloxane, and this represents an effective approach as long as the catalyst composition is placed in an environment free of temperature increases. However, this method is unsatisfactory with regard to the storage stability in the presence of non-neutral substances or in an environment suffering from temperature increases.
Japanese Patent Publication Numbers 46-28795 (28,795/71) and 46-29731 (29,731/71) disclose a platinum/alkenylsiloxane complex catalyst composition which is prepared using phenyl group-containing alkenylsiloxane. However, one encounters very low platinum-based yields in the preparation by conventional methods of platinum complex catalyst compositions having these phenyl-containing alkenylsiloxane ligands, and the problem then arises of poor economics.
In addition, Japanese Patent Application Laid Open (Kokai) Number 56-136655 (136,655/81) proposes a method for the preparation of a platinum/alkenylsiloxane complex catalyst composition via the bis-(1,5-cyclooctadiene)/Pt complex by ligand exchange with siloxane which contains the alkyl and alkenyl groups. Again, the economics of this method are poor due to the low yield of the intermediate bis-(1,5-cyclooctadiene)/pt complex and due to the reduction in yield arising from the rapid decomposition to platinum black when this intermediate's solution comes into contact with the air.
Thus, as discussed above, there have already been various attempts at improving the storage stability of Pt/alkenylsiloxane complex catalyst compositions. Nevertheless, aside from storage in a neutral medium in a low temperature ambient, no Pt/alkenylsiloxane complex catalyst composition has been discovered which evidences an excellent storage stability as well as good economics, nor has a method for the preparation of same been discovered.